This invention relates to a device for controlling the movement position of a moving member, such as a shifter which is mounted in an image forming apparatus and which switches output positions of recording paper. In particular, this invention relates to an improvement for setting a moving member to a predetermined reference position (e.g. an origin at one end of its range of movement) with a simple arrangement.
To start with, brief description is made of a conventional image forming (copying) operation by an electrophotographic image forming apparatus as represented by a digital photocopier. First, an original which is stacked on an automatic document feed tray (hereinafter referred to as original tray) is fed into a scanner unit. The scanner unit reads image data of the original, based on which an electrostatic image is formed on a photosensitive drum. On this photo-sensitive drum, the image data are visualized by toner which attaches to the electrostatic image. Next, recording paper which is transported through a paper transport path passes between the photosensitive drum and a transfer roller, so that the toner image on the photosensitive drum is transferred to the surface of the recording paper. Later, while the recording paper passes by a fuser roller, the fuser roller applies heat and pressure so as to fuse the toner image on the recording paper. After the image is formed in this manner, the recording paper is ejected through an output path to an output tray.
Among this type of image forming apparatus, some are equipped with a shifter mechanism. For example, to make a plurality of copies from a single set of originals, the shifter mechanism serves to eject each set of recording paper at different positions on the output tray. Namely, output positions for the respective sets of recording paper are offset from each other in a horizontal direction which is orthogonal to a paper output direction. Owing to the offset output, the recording paper can be picked up from the output tray and readily sorted into the respective sets. As such, Japanese Patent Application Laid-open No. H4-204668 (JP 4-204668 A) discloses an output tray which is movable in horizontal directions which are orthogonal to a paper output direction. In a copying operation for more than one kind of originals, an OC cover (an original cover) is opened and closed in order to change originals. The output tray is arranged to move in conjunction with such opening and closure of the OC cover.
With respect to a shifter mechanism, the shifter mechanism is required to recognize the position of a shifter (a moving member), to switch positions of the shifter in conjunction with a paper output operation, and to set proper output positions of recording paper on the output tray. For this purpose, the shifter position at power-on or force-reset has to be recognized correctly. In the past, a shifter position sensor (a sensor, microswitch or the like based on an optical means) is incorporated to recognize the shifter position. Such a shifter position sensor detects the shifter position at power-on or force-reset, and if the shifter is out of a predetermined reference position, the shifter is moved to the reference position.
Nevertheless, the above conventional arrangement needs a special sensor for detecting the shifter position, and hence a greater number of components. Eventually, the position control device has a complicated structure and demands a higher production cost.
This invention is made in view of the above concerns. An embodiment of the invention provides a position control device for a moving member which can set a moving member (a shifter) to an exact position without a special sensor.